Poly(.alpha.-olefin)s are known to be those polymers having thermal resistance, rigidity and other properties that are largely influenced by their stereoregularity and regioregularity. Therefore, the performance of poly(.alpha.-olefin)s depends largely on the stereoselectivity and regioselectivity of the catalyst used for .alpha.-olefin polymerization.
Here, the regioselectivity in isotactic polymerization of propylene is evaluated as a proportion of 1,2-inserted monomers (1,2-insertion, primary insertion) to all the propylene monomers inserted. Besides 1,2-insertion, there are 2,1-insertion or secondary insertion and 1,3-insertion (Macromolecules, 1988, 21, 617)(hereafter, the disturbance in regioregularity is referred to as regiodefect).
By the term "2,1-insertion" is meant a linkage containing a 1,2-insertion which includes inserted therein a propylene monomer whose methyne group is bonded to the metal group of a catalyst to form a series of methyne groups bonded together. ##STR2##
The 2,1-insertion includes two types of configurations, i.e., racemic type and meso type in accordance with the difference in enantioface where the 1,2-inserted monomers after the 2,1-insertion coordinate (Polymer, 1992, 33, 254).
By the term "1,3-insertion" is meant that a propylene unit, which is constituted by 3 consecutive methylene units, is inserted in the chain of 1,2-insertions. ##STR3##
In the isotactic polymerization of propylene with a metallocene catalyst (a catalyst comprised of a metallocene compound and a Lewis acid compound such as methylaluminoxane), the resulting polymer have low melting point compared with the isotactic polypropylene obtained with Ziegler-Natta catalyst, due to existence of regiodefect defects although both the polymers have the same stereoregularity (J. Mol. Cat. 56 (1989) 237). Therefore, in the isotactic polymerization of propylene with a metallocene catalyst, catalyst systems are desired which exhibit increased regioselectivity as well as stereoselectivity.
On the other hand, in the polymerization of .alpha.-olefin with a metallocene catalyst, it is known that the stereoregularity and regioregularity of polymers vary considerably depending on the structure of the ligands to the metallocene compound (Macromolecules, 1988, 21, 617; Organometallics, 1994, 13, 964; Angew Chem. Int. Ed. Engl., 1995, 34, 1143).
Japanese Patent Application (Kokai) No. 61-130314 (U.S. Pat. No. 4,769,510) and Japanese Patent Application (Kokai) No. 63-295607 (European Patent No. 284,708) disclose rac-ethylidenebis(1-indenyl)zirconium dichloride, rac-ethylidenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride, rac-dimethylsilylenebis(1-indenyl)zirconium dichloride and other C.sub.2 symmetrical type metallocene compounds represented by the following general formula (5) ##STR4##
The metallocene compounds give rise to isotactic polypropylene in the presence of methylaluminoxane or other Lewis acid promoter. However, isotactic polypropylene polymers obtained using the metallocene compound under the conditions above 25.degree. C. that are useful industrially have low molecular weight and insufficient stereoregularity and regioregularity so that the polymer has low melting point. Therefore, the product is unsuitable for high rigid, high melting point isotactic polypropylene useful as an industrial material.
Thereafter, with view to improving the stereoregularity, molecular weight and the like of polymer, various C.sub.2 symmetrical metallocene compounds having introduced therein one or more substituent groups in its indene ring, represented by the following general formula (6) have been proposed (Japanese Patent Application (Kokai) No. 4-268307 (U.S. Pat. No. 5,243,001), Japanese Patent Application (Kokai) No. 4-268308 (U.S. Pat. No. 5,239,022), Japanese Patent Application (Kokai) No. 4-300887 (U.S. Pat. No. 5,145,819), Japanese Patent Application (Kokai) No. 5-306304 (U.S. Pat. No. 5,304,614), Japanese Patent Application (Kokai) No. 6-184179 (U.S. Pat. No. 5,455,366), Japanese Patent Application (Kokai) No. 7-2920 (European Patent No. 615,981), Japanese Patent Application (Kokai) No. 7-149815 (European Patent No. 646,604), and Japanese Patent Application (Kokai) No. 5-209014 (U.S. Pat. No. 5,296,434). ##STR5##
Specifically disclosed are those C.sub.2 symmetrical type metallocene compounds represented by the general formula (6) in which R.sup.19 =R.sup.20, R.sup.21 =R.sup.22, R.sup.23 =R.sup.24, R.sup.25 =R.sup.26, R.sup.27 =R.sup.28, and R.sup.29 =R.sup.30 and R.sup.19 and R.sup.20 are both a methyl group or an ethyl group.
In particular, Japanese Patent Application (Kokai) No. 6-100579 (European Patent No. 576,970) discloses those C.sub.2 symmetrical type metallocene compounds in which R.sup.23 and R.sup.24 are both an aryl group. The isotactic polypropylene polymerized using the compound as a catalyst component was an isotactic polypropylene having an improved stereoregularity and a relatively high melting point.
However, the product was insufficient to be high rigid, high melting point isotactic polypropylene useful as an industrial material due to the existence of regiodefects in the polymer chain.
Also, Japanese Patent Application (Kokai) No. 7-286005 (European Patent No. 629,632) discloses those C.sub.2 symmetrical type metallocene compounds represented by the general formula (6) in which R.sup.19 and R.sup.20 are both a primary hydrocarbon group (a hydrocarbon group which is bonded to the indene ring through a carbon atom in CH.sub.2 unit (the 1-position atom according to IUPAC rules for the nomenclature of organic compounds) such as an ethyl group, a n-propyl group or an i-butyl group. However, the isotactic polypropylene polymerized using this type of metallocene compound as a catalyst component is also insufficient as high rigid, high melting point isotactic polypropylene useful as an industrial material due to the existence of regiodefects in the polymer chain.
As a metallocene catalyst for isotactic polymerization of .alpha.-olefins, there have been known C.sub.1 symmetrical type metallocene compounds having no symmetry axis in addition to the above-mentioned C.sub.2 symmetrical type metallocene compounds.
Of the C.sub.1 symmetrical type metallocene compounds represented by the general formula (6) in which two indenyl groups are different from each other, there have been disclosed those compounds of formula (6) in which R.sup.19 and R.sup.20 are combinations of a hydrogen atom, a methyl group and an ethyl group (Japanese Patent Application (Kokai) No. 8-67689 (U.S. Pat. No. 5,532,396)). However, the isotactic polypropylene polymerized using the C.sub.1 symmetrical type metallocene compound as a catalyst component had insufficient stereoregularity and regioregularity so as to be useful as a high rigid and high melting point industrial material.